Pass correct context to replaced element

[zbarbuto]

All other element renderers are passed newContext as their RenderContext - the context which has the appropriate styles for the element applied. However, ReplacedElement seemed to miss this change, meaning things like img tags did not get custom styles.

For example, without this change, an element like this:

      <img style="border: 4px solid teal;" src="https://www.google.com/images/branding/googlelogo/2x/googlelogo_color_92x30dp.png">

With an appropriate Container wrapping the network image:

Container(
  border: context.style.border,
  child: image,
);

Would render as:

With this change it can be rendered as expected:

[erickok]

LGTM but I want to regression-test it before merging.